Both the Pirates and Cardinals held the lead in the division earlier this season but have plummeted since, falling 15 1/2 and 10 games, respectively, behind the first-place Milwaukee Brewers.
On Wednesday in Pittsburgh, Aaron Thompson combined with three other pitchers on a five-hit shutout as the Pirates took a 2-0 win over Milwaukee to split a four-game series.
Thompson made his MLB debut and over 4 1/3 innings he gave up four hits and two walks with a strikeout. Jason Grilli (1-0) pitched 2 2/3 perfect innings to get the win while Jose Veras and Joel Hanrahan each worked an inning with Hanrahan getting his 32nd save of the season.
It was L.A.'s first road three-game sweep of the Cardinals since August 1993.
Jaime Garcia (10-7) dropped his third straight decision after allowing seven runs on nine hits over just five innings.
Getting the call for St. Louis tonight will be right-hander Edwin Jackson, who's 2-0 in three career starts against the Pirates with a 3.79 earned run average in 19 innings.
Jackson started the season with 19 appearances for the Chicago White Sox before heading to the Cardinals at the trading deadline. He's 2-2 in five starts since the deal, beating the Chicago Cubs and Colorado Rockies, while losing to Milwaukee and the Cubs.
He was 7-7 with the White Sox with a 3.92 ERA.
Jackson's given up three runs or less seven times in his last 10 starts while pitching at least six innings nine times.
For the Pirates, righty Charlie Morton can extend a four-start unbeaten streak. The 27-year-old last lost on July 29 at Philadelphia, when he was touched for nine hits and eight runs in four innings of a 10-3 loss.
He's won once and gotten three no-decisions since while surrendering just three combined runs in 28 1/3 innings against the Cubs, San Francisco, Milwaukee and Cincinnati.
The Pirates are 2-2 in the four games.
Morton is 2-3 in seven lifetime starts against the Cardinals with a 6.21 ERA.
Pittsburgh is 5-4 versus the Cardinals this season.